Concentric-ground cable presents several problems to anyone who wants to locate any of its high resistive-ground faults using one of the conventional fault Iocators presently available. Three of these problems are as follows:
1. Most locators suffer from the shielding effects produced by this type of cable's manufactured co-axial configuration. PA1 2. Most locators suffer from the excessive loading effects put on them by this type of cable's high interconductor capacity. PA1 3. Most locators with their relatively low signal voltages have difficulties detecting the presence of any of this type of cables ground-faults because of their excessively high resistance values result in them producing a very small fault current. PA1 1. A trace-signal generator the output of which maximizes the resistive-fault current of the cable in a way that minimizes the associated capacitive-reactive current of the cable. PA1 2. A trace-signal generator that is portable and capable of operating from some form of a conventional type battery supply. PA1 3. A trace-signal receiver that is exclusively dedicated to the signal of the generating transmitter, thereby offering interference free and noise free operation, plus being portable and battery operated.
Because of the factors listed above, most magnetically linked fault Iocators cannot detect the locations of the majority of ground-faults that occur on concentric-ground cables. Consequently the two major methods in use today are pulse reflection (VSWR), and/or high voltage DC thumping (blow-out). Pulse-reflection methods can only locate faults to within 25 to 50 feet, and HV DC thumping, though it is geometrically accurate inflicts considerable damage on the cable. These difficulties have perpetuated the need for a simpler method of detecting the location of a fault in a cable of this type using a device which is readily portable and hence can be carried over a cable path by a walking operator.
Any fault locator system that is going to stand a chance of performing this task must overcome all the problems created by concentric-ground cables, and should also conform to the following basic requirements, that is it should have:
Reference is made to the design shown in my earlier U.S. Pat. No. 4,387,337, although this is only because some of the techniques of that patent fit the unique requirements created by concentric-ground cables and their associated high resistance ground-faults.